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## 4th grade

### Course: 4th grade > Unit 8

Lesson 5: Adding and subtracting mixed numbers- Adding mixed numbers with like denominators
- Subtracting mixed numbers with like denominators
- Add and subtract mixed numbers (no regrouping)
- Mixed number addition with regrouping
- Subtracting mixed numbers with regrouping
- Add and subtract mixed numbers (with regrouping)

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# Mixed number addition with regrouping

Sal practices adding mixed numbers with common (like) denominators. Items require regrouping.

## Want to join the conversation?

- is there an easier way to add?(11 votes)
- this is a wayA Rhyme To Help You Remember

♫ "If adding or subtracting is your aim,

The bottom numbers must be the same!

♫ "Change the bottom using multiply or divide,

But the same to the top must be applied,

♫ "And don't forget to simplify,

Before its time to say good bye"(53 votes)

- If you are alive like this post(14 votes)
- it is a little confusing(7 votes)
- I think that this really helped me and I'm a math matision(8 votes)
- It's mathematician not math matision.(2 votes)

- this is soooo confusing 🤔 🤔 🤔 🤔 🤔 🤔! ! ! ! ! !(6 votes)
- This is confusing for me, can someone help me?🤔🤔🤔🤔(4 votes)
- Yes. The addition can be easily done if you convert it into a improper fraction, then get them common denominators, and then add them.(4 votes)

- this is so hard! I need help!(3 votes)
- dont panic just relax and keep trying and dont overthink it(4 votes)

- just try to like focus(4 votes)
- this was so helpful thank you so much Sal khan(4 votes)
- I tried on a khan question but didnt work, it said it needed to be simplified!!1!1! grrrr😡😡😡😡😡(3 votes)

## Video transcript

- [Narrator] Let's see if we can add five and 2/5 to three and 4/5. Pause this video and see if you
can figure out what this is. All right, now let's do this together. We've had a little bit of practice adding mixed numbers in the past. And so one way to think about it is, you could view five and
2/5 as five plus 2/5. And then to that we're going
to be adding three and 4/5, which you could view as three plus 4/5. And then you could just change the order with which you are adding, and say, all right, well, I could say five plus three, so that's five plus three, and then to that I could add 2/5 and 4/5, so, plus 2/5, plus 4/5. Now what is that going to get me? Well five plus three is
going to be equal to eight. Eight plus, and then if I have 2/5, and I add four more fifths to that, well now I'm going to have 6/5. Two of something plus
four of that something is going to be six of that something, and the something in this case are fifths. So now I'm going to have 6/5. So some of you might be tempted to say, "Hey, isn't this just going to be equal to eight and 6/5?" And you wouldn't be completely
wrong if you said that. But pause this video and think about why this feels a little bit off. Well, the reason why this isn't standard, is the fractional part
of this mixed number 6/5 is greater than one. So there's a whole inside of this 6/5. So the standard way to do this is see if we can break out that whole. Now what do I mean by that? Well I could rewrite eight plus 6/5 as eight plus 6/5 is the same thing as a whole, or 5/5 plus 1/5. And why is this useful? Well 5/5 is the same thing as one. And so now I can say
this is going to be equal to eight plus one whole is nine, that's eight plus the 5/5, and then what I have leftover is 1/5. So nine and 1/5. And so this is the direction that people will traditionally go in. Now there's another way
that you could approach it, which is really the same idea, we're just writing things
a little bit differently. We could write this as five and 2/5 plus three and 4/5, and notice the way that I wrote it. I put all the fractions
in the fraction column, I guess you could call it that way, and I put all of our whole
numbers underneath each other, and if I had multiple digits here, I would align them
according to place value. And then what we could do is we could say, okay 2/5 plus 4/5 is going to be 6/5. We could write 6/5 there. But we say, hey, there's
something a little bit fishy about 6/5. That's really the same
thing as 5/5 plus 1/5, or you could say that's the
same thing as one and 1/5. 6/5 is equal to one and 1/5, and so what you could do is, you could write the 1/5 part
in the fractions column, and then the one well now you're
going to be regrouping that into our whole numbers, so you put a one right over there. Notice, 2/5 plus 4/5 is one and 1/5, which is the same thing as 6/5. And then you add the whole number part. One plus five plus three is nine. So you get nine and 1/5. But hopefully you realize that these are really the same idea, just different way of writing things